This invention relates to an opening unit for open-end spinning machines comprising an opening roller lined with sawtooth wire; a housing which surrounds this roller closely over part of its periphery; a delivery slot in the housing; a fibre guide duct following the housing in the direction of rotation of the opening roller and a dirt separation duct under reduced pressure which is situated between the delivery slot and the fibre guide duct.
In one known opening unit of this type, any particles of dirt present in the fibres are projected by centrifugal force into the dirt separation duct and are therefore unable to enter the spinning turbine. However, since the fibres entrained by the opening roller no longer have any hold in the region of the dirt separation duct, they are in danger of being removed from the opening roller by the centrifugal force and the slight reduced pressure prevailing in the dirt separation duct so that the quality of the yarn can be adversely affected.
The object of the present invention is to provide an opening unit of the type mentioned at the beginning in which the unfavourable effect of the dirt separation duct is avoided.